The improvement of soil thermodynamics and its effects on land surface meteorology in the IPSL climate model
Résumé
This paper describes the implementation of an improved soil thermodynamics in 9 the hydrological module of Earth System Model (ESM) developed at the Institut 10 Pierre Simon Laplace (IPSL) and its effects on land surface meteorology in the IPSL 11 climate model. A common vertical discretization scheme for the soil moisture and for 12 the soil temperature is adopted. In addition to the heat conduction process, the heat 13 transported by liquid water into the soil is modeled. The thermal conductivity and the 14 heat capacity are parameterized as a function of the soil moisture and the texture. 15 Preliminary tests are performed in an idealized 1D framework and the full model is 16 then evaluated in the coupled land/atmospheric module of the IPSL ESM. A nudging 17 approach is used in order to avoid the time-consuming long-term simulations required 18 to account for the natural variability of the climate. Thanks to this nudging approach, 19 the effects of the modified parameterizations can be modeled. The dependence of the 20 soil thermal properties on moisture and texture lead to the most significant changes in 21 the surface energy budget and in the surface temperature, with the strongest effects on 22 the surface energy budget taking place over dry areas and during the night. This has 23 important consequences on the mean surface temperature over dry areas and during 24 the night and on its short-term variability. The parameterization of the soil thermal 25 properties could therefore explain some of the temperature biases and part of the 26 dispersion over dry areas in simulations of extreme events such as heat waves in 27 state-of-the-art climate models.
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